The invention relates generally to electric solenoid valves for controlling intermittent fluid flow and methods therefor, and more particularly to electric solenoid valves useable for intermittently dispensing relatively high viscosity fluids including hot melt adhesives.
The intermittent dispensing of viscous fluids with an electric solenoid valve having an armature reciprocatably disposed in a housing is known generally and has many applications. Hot melt adhesives for example are dispensed to seal cardboard cartons and other packaging, referred to herein generally as a substrate, in assembly-line operations, wherein typically a plurality of individually actuatable electric solenoid valves are coupled to a common manifold to form a modular adhesive dispensing assembly. The compactness of many modular assemblies is promoted by supplying fluid to a side portion of the housing of each electric solenoid valve, substantially transverse to the armature axis, rather than from along an axial end of the armature.
Hot melt adhesives and other heated viscous fluids have a tendency to degrade rapidly when allowed to stagnate, as occurs frequently in intermittent dispensing applications, particularly in electric solenoid valves having non-linear fluid flow paths, which tend to generate fluid flow eddies and regions of little or no flow. The transversely disposed fluid inlets found on many modular assemblies are thus particularly susceptible to undesirable fluid stagnation.
U.S. Pat. No. 5,172,833 entitled "Modular Applicator Having A Separate Flow Loop To Prevent Stagnant Regions" issued on Dec. 22, 1992 to Faulkner III discloses an electric solenoid valve module having an armature reciprocatably disposed in a guide tube. Fluid is dispensed from an outlet port of the module by unseating a spherical end portion of the armature from a seat upon energizing the solenoid. A fluid inlet located on a top side of the module supplies fluid radially inwardly to an adhesive chamber disposed about the armature, wherein fluid flows divergently in oppositely directed high and low volume flow paths. The high-volume flow path is along the armature toward the spherical end portion thereof near the module outlet port, and the low-volume flow path is along the armature toward an opposing end thereof, near a pole-piece of the solenoid. The low-volume flow path circulates through a bore of the armature and then back toward the spherical end portion thereof where it reunites with the high-volume flow path, thereby circulating fluid to reduce stagnation.
In some hot melt adhesive dispensing applications the fluid is dispensed continuously to form continuous adhesive beads on the substrate where bonding is required, and in other applications the fluid is dispensed intermittently to form a series of adhesive dots on the substrate. The latter, intermittent fluid dispensing operations provide, among other advantages, economized adhesive usage and reduced heat transfer to the substrate. Intermittent fluid dispensing operations however require relatively short valve opening and closing times, or increased actuation responsiveness, particularly where smaller adhesive dot formation is required and in applications having relative high velocities between the substrate and fluid dispensing valve.
U.S. Pat. No. 4,951,917 entitled "Dynamic Response Time For Electromagnetic Valving" issued on Aug. 28, 1990 to Faulkner III discloses an armature having an upstream end with C-shaped raised lips disposed peripherally thereon relative to a recessed region, wherein the raised lips abut a pole piece of the solenoid against the bias of a compressed spring therebetween when the solenoid is energized. The C-shaped raised lips of the armature allegedly reduce closing response time by facilitating migration of viscous fluid between the armature and the pole piece when the solenoid is de-energized, wherein fluid re-circulates back toward the end of the armature along longitudinal grooves disposed peripherally thereon. However, the recessed region on the end of the armature and the longitudinal grooves along the peripheral sides of the armature reduce the sectional area of the armature end thereby reducing the magnetic attraction between the pole piece and the armature, which adversely affects valve opening response time when the solenoid is energized.
The present invention is drawn toward advancements in the art of electric solenoid valves, and more particularly to electric solenoid valves useable for intermittently dispensing relatively high viscosity fluids including hot melt adhesives.
It is thus an object of the invention to provide novel electric solenoid valves and methods therefor that overcome problems in the prior art.
It is also object of the invention to provide novel electric solenoid valves and methods therefor that reduce fluid stagnation, that provide improved actuation responsiveness, particularly during intermittent fluid dispensing operations, that are integrateable with fluid dispensing systems, that are retrofittable on existing fluid dispensing assemblies, and that are economical and reliable.
It is another object of the invention to provide novel electric solenoid valves and methods therefor, wherein the electric solenoid valve comprises generally an armature reciprocatably disposed in an axial bore of a housing member having a fluid inlet and a fluid outlet coupled to the axial bore at a first end thereof. The armature includes a valve member disposed at a first end portion thereof, and a magnetically attractable second end portion defining a second end of the armature disposed toward a relatively fixed core portion of the solenoid. The armature includes an interior fluid passage with a fluid inlet disposed between the fluid inlet of the housing member and the second end of the armature to couple the interior fluid passage with the fluid inlet of the housing member. A fluid outlet is disposed proximate the valve member of the armature and is coupleable to the fluid outlet of the housing member when the valve member is unseated from a valve seat disposed along the axial bore proximate the fluid outlet of the housing member.
It is a more particular object of the invention to provide novel electric solenoid valves and methods therefor that reduce fluid stagnation by circulating fluid supplied to the axial bore of the housing member to a fluid inlet of the armature disposed between the fluid inlet of the housing member and the second end of the armature, and circulating fluid from the interior passage of the armature toward a fluid outlet of the armature disposed proximate the valve member thereof. The valve member of the armature is seated on a valve seat of the housing member to obstruct fluid flow from the fluid outlet of the housing member, and the valve member of the armature is unseatable from the valve seat to permit fluid flow from the fluid outlet of the housing member.
It is also a more particular object of the invention to provide novel electric solenoid valves and methods therefor that reduce fluid stagnation by isolating the fluid outlet of the armature from the axial bore of the housing member with a substantially fluid impermeable seal formed between the first end portion of the armature and the housing member, whereby fluid supplied from the fluid inlet of the housing member is directed toward the fluid inlet of the armature, and additionally by circulating fluid along a secondary fluid flow path about the second end of the armature into the interior fluid passage thereof.
It is another more particular object of the invention to provide novel electric solenoid valves and methods therefor that provide improved actuation responsiveness during intermittent fluid dispensing operations by any one or more of the following. Increasing an area of the second end of the armature facing toward the core portion of the solenoid, increasing the magnetic attraction between the armature and the fixed core portion of the solenoid by forming the fluid inlet of the armature away from the second end of the armature, forming an intermediate portion of the armature of a non-magnetically attractable tubular portion, which is lightweight relative to the magnetically attractable second end portion of the armature, and disposing a non-magnetically attractable shim between the end of the fixed core portion of the solenoid and the second end of the armature to facilitate separation of the armature from the fixed core portion upon de-energizing the solenoid.
These and other objects, features, aspects and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced generally by corresponding numerals and indicators.